Rh84 built, first impressions

[dowto1000]

A dc version of the RH would be interesting, sounds like a fun build.

That is what I have designed the last two weeks, except with a tube that sounds better than a 6BQ5, ie, a 6AQ5, and a direct couple, and a " LSES " Low Storage Effect Supply, which chokes at 20 Ohms or less, and the input tube gas-tube B+ regulated. Got it designed, building it is next.

Dowto1000

 

[Tubeglowpio]

That is what I have designed the last two weeks, except with a tube that sounds better than a 6BQ5, ie, a 6AQ5, and a direct couple, and a " LSES " Low Storage Effect Supply, which chokes at Ohms or less, and the input tube gas-tube B+ regulated. Got it designed, building it is next.

Dowto1000

If you end up liking it let me know, I would like to try it out especially if youre telling me it would beat the 2a3 amp we talked about. I need to build some better speakers soon though if I want to get the most out of a DC amp.

 

[primosounds]

I used a 2.2k for each channel as shown on the schematic. That was measured from ground though so wouldn't it be about 10-13 volts less to the cathode then? I figured it would be ok with that type of tube because plenty of people triode strap el84 tubes around that voltage anyways, more curious if you got the same results on one of your version 1 rh84 amps? I should see what it reads in ul mode.

It is not a super big deal but you could go with a 2.5K or 3K to bring it closer to the 250v max. On my own builds if i have a choke that can handle about 40ma of around 500 ohms dcr i would place it in the G2 supply and that makes an audible difference.

 

[Tubeglowpio]

It is not a super big deal but you could go with a 2.5K or 3K to bring it closer to the 250v max. On my own builds if i have a choke that can handle about 40ma of around 500 ohms dcr i would place it in the G2 supply and that makes an audible difference.

I like the choke idea, will have to try that next time, why 500 ohms though and not one around 1k? Even though I have that 2.2k there since it's really close to same potential as the plate it's basically in triode mode then correct? Maybe that's why it doesn't have as much grunt in the low end.

 

[primosounds]

I like the choke idea, will have to try that next time, why 500 ohms though and not one around 1k? Even though I have that 2.2k there since it's really close to same potential as the plate it's basically in triode mode then correct? Maybe that's why it doesn't have as much grunt in the low end.

. Not really. Pentode mode has the highest output of all. If you have not upped the input grid to ground resistor to at least 500k, i would guess that maybe part of that low output issue.
The choice of the choke to help regulate the G2 supply is based on the current demand and being above critical inductance, and being able to fit under the chassis. There is usually more space below than above the chassis. For the rh84 the choke doesn't need to supply much current , something around 25ma ( at 250v Av and G2, current for G2 is about 6ma per tube) is more than enough for 2 6bq5 + tapping the at7 B+ from there. I usually add a film cap of around 5uf after the choke.

 

[dowto1000]

TGPIO,

I think Primosounds has given you good advice, to up the grid to ground value to 1/2 a Meg or so !! I think that should be your first priority change. Add 400K to the ground return of the 100K pot, but only as a temporary change ( two resistances in series doesn't sound as good as one resistive element ) - or go to a 500K pot to have more gain choice.

I hate POTS on the input of an amp. Sonic losses are far too large. I usually use about 375K for grid to ground, in a high impedance two-stage amp circuit, and a HIGH quality resistor like a quiet Caddock TF-020

Dowto1000

 

[Tubeglowpio]

TGPIO,

I think Primosounds has given you good advice, to up the grid to ground value to 1/2 a Meg or so !! I think that should be your first priority change. Add 400K to the ground return of the 100K pot, but only as a temporary change ( two resistances in series doesn't sound as good as one resistive element ) - or go to a 500K pot to have more gain choice.

I hate POTS on the input of an amp. Sonic losses are far too large. I usually use about 375K for grid to ground, in a high impedance two-stage amp circuit, and a HIGH quality resistor like a quiet Caddock TF-020

Dowto1000

Ill give it a try this weekend and see what's best then get the correct pot. Are those metal film?

 

[dowto1000]

You can look up what a Caddock TF-020 is can't you ??

Let me ask you a question. Do you have a Preamp, or some sort of way to control VOLUME, going into the RCA input jacks of this amplifier?? If so, it is needless and not smart at all to put a POT on the input jack, the LOWEST level circuitry of the entire amp.

In fact, GOOD amps, well designed ones, should have no user pots, or adjustments, what so ever, if you want maximum reliability and best possible sound. Let me say that again: In fact, GOOD amps should have no user pots what so ever, if you want maximum reliability and best possible sound. I am including a HUM pot on a DHT like a 2A3 also kiddies. I never will use them and all the added wiring, etc etc etc.

If you have a controllable volume source, I will mail you a pair of quiet Rs in the 250K to 500K range, that will be entirely suitable to put across your RCA input jack, as a path to ground. They are a gift, and IF I mail on Thursday, they will reach you by Saturday's mail. Let me know ASAP, and PM me your mailing address. ' Hear that !!

Dowto1000

 

[Tubeglowpio]

You can look up what a Caddock TF-020 is can't you ??

Let me ask you a question. Do you have a Preamp, or some sort of way to control VOLUME, going into the RCA input jacks of this amplifier?? If so, it is needless and not smart at all to put a POT on the input jack, the LOWEST level circuitry of the entire amp.

In fact, GOOD amps, well designed ones, should have no user pots, or adjustments, what so ever, if you want maximum reliability and best possible sound. Let me say that again: In fact, GOOD amps should have no user pots what so ever, if you want maximum reliability and best possible sound. I am including a HUM pot on a DHT like a 2A3 also kiddies. I never will use them and all the added wiring, etc etc etc.

If you have a controllable volume source, I will mail you a pair of quiet Rs in the 250K to 500K range, that will be entirely suitable to put across your RCA input jack, as a path to ground. They are a gift, and IF I mail on Thursday, they will reach you by Saturday's mail. Let me know ASAP, and PM me your mailing address. ' Hear that !!

Dowto1000

Of course I could look it up, just thought you would know if you already use them. If I use a metal film it would be a non inductive type. I'll check and see the one you mention, hopefully mouser has them. I don't have a preamp because all of my amps are two stage with enough gain, like I said this is for my dad and I'm giving it to him on the 4th of July, it was supposed to be all in one no preamplifier. He will use a computer or CD player which will have more gain then my phone. Im also finishing burning the amp in before I do anything, I have already noticed massive improvements, voices are finally smooth and soundstage is great and bass is better now and tight. Only 12 hours on it and it has changed a lot. It's not just my ears adjusting either because I had my wife hear it the first hour and she hated it and left after 10 minutes then didn't hear it till the 10th hour tonight and she loves it now and thought it was smoother, slightly warm, 3d and involving. She is my test subject so I can know it's not my ears messing with me. All is good, so thanks to both of you and glad I trusted primos recommendation of this circuit, no wonder you've built several. I already to my dad how hard it will be to let it go but I know he will take care of it. His favorite song is thorn tree in the garden by Derek and the dominoes which I've always thought that song didn't sound good on most systems as in not the best recording but this one is sweet enough to handle it well.

 

[dowto1000]

Of course I could look it up, just thought you would know if you already use them. If I use a metal film it would be a non inductive type. I'll check and see the one you mention, hopefully mouser has them. I don't have a preamp because all of my amps are two stage with enough gain, like I said this is for my dad and I'm giving it to him on the 4th of July, it was supposed to be all in one no preamplifier. He will use a computer or CD player which will have more gain then my phone. Im also finishing burning the amp in before I do anything, I have already noticed massive improvements, voices are finally smooth and soundstage is great and bass is better now and tight. Only 12 hours on it and it has changed a lot. It's not just my ears adjusting either because I had my wife hear it the first hour and she hated it and left after 10 minutes then didn't hear it till the 10th hour tonight and she loves it now and thought it was smoother, slightly warm, 3d and involving. She is my test subject so I can know it's not my ears messing with me. All is good, so thanks to both of you and glad I trusted primos recommendation of this circuit, no wonder you've built several. I already to my dad how hard it will be to let it go but I know he will take care of it. His favorite song is thorn tree in the garden by Derek and the dominoes which I've always thought that song didn't sound good on most systems as in not the best recording but this one is sweet enough to handle it well.

Well, its good that you are happy and its breaking in !! Its a relief for all of us. Lesson learned by you. BTW, you still need to raise the grid to ground.

I should advise you, that ALL you are hearing now, is the advantage of a ( KISS ) two stage tube amp circuit, over a more complex and thus signal-degrading three stage amp.

The Rh84 circuit has two huge ( IMHO ) negatives Jake, which both need to be avoided. They are each, individually, poison, and combined as BOTH, in the Rh84 circuit, leave much to be desired, in terms of possible-to-obtain audio performance :

(1) First, the Rh84 employs a negative feedback loop, back to the input tube, which injects out-of-time signals to the incoming music. The world's best sounding tube audio ( and SE amps ) won't have a NFB loop.

(2) Second, It uses a capacitor, as a means of coupling the first stage to the second. The coupling cap should not be in the two-stage amp.

Caps are the worst part in audio, They are " all over the place " in how they play various parts of the music spectrum. No one cap does it all.

In the case of a simple two stage amp, always use a carefully chosen high-quality span of wire, a simple direct couple of the signal, first stage to the second, to eliminate driving though a capacitor. The Rh84 design, could be, and should be, re-designed as a direct couple. Again Jake, ( KISS ).

I will refer you to the two attachments in post number 44 in the current 6AQ5 thread, on Page 3.


http://audiokarma.org/forums/index....esign-guys-why-no-love-for-6aq5.287222/page-3


Those two attachments combined, shows a topology that totally avoids both of Rh84's circuit goof ups, and this that I am suggesting Jake will **** easily ***** out-perform musically, any and all Rh84s .

Consider your Rh84 build a simple learning experience, ( "two stage versus three stage amps" ) enjoy it for the moment, and move on to hearing the better topologies, with less degradation of the audio signal, is my suggestion to you.

Have fun. I do.

Dowto1000.

 

[dowto1000]

What would the plate and cathode voltages be when using an EL84/6BQ5 type?

Don't use an EL84 or a 6BQ5,....... use only a 6AQ5 or a 6005 !! ' Better sounding tube.

I am so sorry, but I am not going to give that information out.

I have provided you with the architecture, you select the OP points.

That Gas Regulator tube is optional - not required to do the Direct Couple.

Be conservative, you see I use 62% of rated plate dissipation on the Finals, ( 62% is Golden Ratio ) reducing current, not voltage, and learn to direct couple it on your own.

I guarantee you, if you put in some effort, some " skin", you will get something NICE out of this !!


Dowto1000

 

[Tubeglowpio]

Well, its good that you are happy and its breaking in !! Its a relief for all of us. Lesson learned by you. BTW, you still need to raise the grid to ground.

I should advise you, that ALL you are hearing now, is the advantage of a ( KISS ) two stage tube amp circuit, over a more complex and thus signal-degrading three stage amp.

The Rh84 circuit has two huge ( IMHO ) negatives Jake, which both need to be avoided. They are each, individually, poison, and combined as BOTH, in the Rh84 circuit, leave much to be desired, in terms of possible-to-obtain audio performance :

(1) First, the Rh84 employs a negative feedback loop, back to the input tube, which injects out-of-time signals to the incoming music. The world's best sounding tube audio ( and SE amps ) won't have a NFB loop.

(2) Second, It uses a capacitor, as a means of coupling the first stage to the second. The coupling cap should not be in the two-stage amp.

Caps are the worst part in audio, They are " all over the place " in how they play various parts of the music spectrum. No one cap does it all.

In the case of a simple two stage amp, always use a carefully chosen high-quality span of wire, a simple direct couple of the signal, first stage to the second, to eliminate driving though a capacitor. The Rh84 design, could be, and should be, re-designed as a direct couple. Again Jake, ( KISS ).

I will refer you to the two attachments in post number 44 in the current 6AQ5 thread, on Page 3.


http://audiokarma.org/forums/index....esign-guys-why-no-love-for-6aq5.287222/page-3


Those two attachments combined, shows a topology that totally avoids both of Rh84's circuit goof ups, and this that I am suggesting Jake will **** easily ***** out-perform musically, any and all Rh84s .

Consider your Rh84 build a simple learning experience, ( "two stage versus three stage amps" ) enjoy it for the moment, and move on to hearing the better topologies, with less degradation of the audio signal, is my suggestion to you.

Have fun. I do.

Dowto1000.

I knew the downsides of this amp for a long time now, was just curious of it's sound and I was ok with it being cap coupled as amps I've built and other classic amps have used them and their sound can be enjoyable to me. I was not going for perfection here if I was it wouldn't have been an rh84 and it would most likely not have had feedback nor would it be a pentode or have non linear tubes, ect... Sometimes it's the imperfections of certain amps that can make the amp more appealing to the ears, most of my builds of been aimed towards this. I'm also totally open to building some that reproduce the music as perfect as possible but I will need to design a whole system to do so as speakers, source, amp will all play a big role in getting that music reproduction. Enjoy it at the moment I will, I'm sure I will tweak and experiment with it more as well. I have listened to several "high end amps" and find a lot of them to be kind of dull, one had a 300b driving a 807 and I not all that impressed, honestly think the Rh beats it in musical experience and top end. It was pretty clean, had somewhat nice midrange and upper bass and a bit warm but the soundstage was very 2d. If I cant get the speakers to disappear and have the music sound sweet and like its floating from different places in the air then it's just not my taste and will end getting rid of it asap or if it did everything else right could use it for background music.

 

[Tubeglowpio]

. Not really. Pentode mode has the highest output of all. If you have not upped the input grid to ground resistor to at least 500k, i would guess that maybe part of that low output issue.
The choice of the choke to help regulate the G2 supply is based on the current demand and being above critical inductance, and being able to fit under the chassis. There is usually more space below than above the chassis. For the rh84 the choke doesn't need to supply much current , something around 25ma ( at 250v Av and G2, current for G2 is about 6ma per tube) is more than enough for 2 6bq5 + tapping the at7 B+ from there. I usually add a film cap of around 5uf after the choke.

Of course pentode has higher output power, was just saying that if the screen is at the same potential as the plate then isn't it basically triode strapped? You can make a pentode work like a triode if you take the screen and connect it to the plate, a lot of people use a 100 ohm to do this and so I was just pointing out that my amp may not be running fully as a pentode due to it's potential being the same.

 

[dowto1000]

I knew the downsides of this amp for a long time now, was just curious of it's sound and I was ok with it being cap coupled as amps I've built and other classic amps have used them and their sound can be enjoyable to me. I was not going for perfection here if I was it wouldn't have been an rh84 and it would most likely not have had feedback nor would it be a pentode or have non linear tubes, ect... Sometimes it's the imperfections of certain amps that can make the amp more appealing to the ears, most of my builds of been aimed towards this. I'm also totally open to building some that reproduce the music as perfect as possible but I will need to design a whole system to do so as speakers, source, amp will all play a big role in getting that music reproduction. Enjoy it at the moment I will, I'm sure I will tweak and experiment with it more as well. I have listened to several "high end amps" and find a lot of them to be kind of dull, one had a 300b driving a 807 and I not all that impressed, honestly think the Rh beats it in musical experience and top end. It was pretty clean, had somewhat nice midrange and upper bass and a bit warm but the soundstage was very 2d. If I cant get the speakers to disappear and have the music sound sweet and like its floating from different places in the air then it's just not my taste and will end getting rid of it asap or if it did everything else right could use it for background music.

Hello !!

A 300B ( too low a gain, NOT a good tube) driving a 807, sound yucckie to me, from what I know of both. Glad you heard that. Was it a three stage amp?? Most tube amps suck. More like tuners than honest amps.

I think you need either ALTEC 604s ( actually.....GPA 604s are best ) in a MLTL or a pair of VOTT A7-8 old movie speakers - which work in a small room, and be done with speakers. If on an extreme budget, I can get you the name of Pro-Sound coaxials, that are silly in cost ( low) and a HUGE bang for the buck. There is nothing in audio like a 15 inch woofer, and a two way, IME.

You really should attend Denver / RMAF this Oct 5-7th.

Dowto1000

 

[Tubeglowpio]

It's not the voltage equivalence that creates the "triode" it's the paralleling of the connection putting the signal on each.

This is what I was wondering, thank you for clearing that up. I should have looked at a schematic before thinking about that one haha, I see that could be the case only if it were connected to the same wire of the output, not sure why I forgot about that.

 

[Tubeglowpio]

Hello !!

A 300B ( too low a gain, NOT a good tube) driving a 807, sound yucckie to me, from what I know of both. Glad you heard that. Was it a three stage amp?? Most tube amps suck. More like tuners than honest amps.

I think you need either ALTEC 604s ( actually.....GPA 604s are best ) in a MLTL or a pair of VOTT A7-8 old movie speakers - which work in a small room, and be done with speakers. If on an extreme budget, I can get you the name of Pro-Sound coaxials, that are silly in cost ( low) and a HUGE bang for the buck. There is nothing in audio like a 15 inch woofer, and a two way, IME.

You really should attend Denver / RMAF this Oct 5-7th.

Dowto1000

It really was not impressive, the dealer there was selling the system to an older couple and they liked it enough to sit down and purchase, I came out of the room and the dealer was outside talking to someone and the guys wife said, "That's some nice sound, huh"? I wanted to cut down the system and tell them not even close to the 7 grand or whatever it was but I didn't feel it was my place to have the dealer lose the sale and different people like different sounds so I left it alone.

 

[Tubeglowpio]

Hello !!

A 300B ( too low a gain, NOT a good tube) driving a 807, sound yucckie to me, from what I know of both. Glad you heard that. Was it a three stage amp?? Most tube amps suck. More like tuners than honest amps.

I think you need either ALTEC 604s ( actually.....GPA 604s are best ) in a MLTL or a pair of VOTT A7-8 old movie speakers - which work in a small room, and be done with speakers. If on an extreme budget, I can get you the name of Pro-Sound coaxials, that are silly in cost ( low) and a HUGE bang for the buck. There is nothing in audio like a 15 inch woofer, and a two way, IME.

You really should attend Denver / RMAF this Oct 5-7th.

Dowto1000

I would love to go to RMAF this year but due to a very busy semester at school coming up I wont be able to, next year though I'll be there.